Boron carbide (B4C) is the third hardest known material behind diamond and the hardest known material which is thermodynamically stable at ambient pressures. High hardness combined with low weight (theoretical density: 2.52 g/cm3) have made boron carbide a preferred material of the strike face for personal armor systems to stop, for example, armor piercing bullets. Such armor is typically manufactured by hot-pressing, which involves uniaxially pressing boron carbide powder in graphite performs with graphite dies at elevated temperatures. While this process produces densified ceramic bodies of adequately low porosity to properly function as armor; hot pressed boron carbide is only economically feasible for the fabrication of simple shapes, which can nest one above the other so that a stack of parts can be simultaneously hot-pressed.
In a recently issued patent, Speyer et al. (U.S. Pat. No. 7,517,491) showed that high purity sinter-grade (median particle size, d50=0.8 μm) boron carbide could be pressurelessly sintered to a closed porosity state in part by extracting the boron oxide layer on particles in the pressed compact. Such articles could then benefit from the densification action of hot isostatic pressing HIPing). These articles reached near theoretical density after HIPing, suffered no shape restriction because of the method of processing, and yielded hardnesses higher than any other reported for boron carbide. The boron carbide powder used by Speyer et al. was high purity, sub micron (d50=0.8 μm), with a broad particle size distribution which facilitated high green relative densities (65-70%).
Pressureless sintering a boron carbide compact that includes a sintering promoter such as carbon is well known. It is also well known that the compact can include titanium compounds such as Mania which is introduced into the compact in powder form prior to forming the compact. See C. S. Wiley, Ph. D. Thesis, Synergistic Methods for the Production of High Strength and Low Cost Boron Carbide, Georgia Institute of Technology, Published December 2011.